This invention relates to the selective separation of certain solids from solid mixtures containing silica or siliceous gangue.
The processing of mixed solids in particulate form is widely practiced in industry. The solids are usually separated into individual components (solid/solid separation) by a variety of engineering processes using inherent differences between the various solid components. These inherent differences include color, size, conductivity, reflectance, density, magnetic permeability, electrical conductivity and surface wettability. This latter characteristic, surface wettability, is exploited in froth flotation, flocculation and agglomeration processes which rely heavily on various chemical treatments to enhance separation.
Differences in the other characteristics identified above, especially size, conductivity, density, magnetic permeability and electrical conductivity, have typically been utilized to obtain separation via various mechanical methods. These methods include the use of screening, wet cyclones, hydroseparators, centrifuges, heavy media devices, desliming vessels, jigs, wet tables, spirals, magnetic separators and electrostatic separators. The proper use of water is recognized as critical to the efficiency of such methods. A fundamental driving force in most of these operations is the control of how particles flow, settle or are magnetically or electrically manipulated in an aqueous environment. Factors such as the density (percent solids by weight) of the solid mixture solutions in water; the degree of mechanical agitation of such pulps; the size of particles in the solid mixtures; and the equipment design and size all act and/or are controlled in a complex fashion to optimize the appropriate solid separation in any specific operation. While some universal scientific and engineering concepts can be applied in such separations, the complexity of such operations frequently requires empirical testing and adjustment to effect a suitable separation.
One area that is well recognized as a requirement of equipment optimization is the proper dispersion of the individual solid particles of the mixtures being fed to such physical separation devices. Separation efficiency drops dramatically when the solid mixture (pulp) is too dense. Conversely, when the percentage of solids is too low, the separation of components may be good, but the solids feed is too small per unit of equipment size to be economically viable.
The role of chemicals in these mechanical separation processes is relatively small. Chemicals that have been used include pH regulators such as caustic and lime; flooculents such as high molecular weight acrylamides; and dispersants such as sodium silicate and polyacrylic acid polymers. The effect of these additives has generally been sporadic and has varied between positive and negative depending on the equipment used, small variations in the dosage, the nature of the solid feed mixtures and so on. The use of such chemicals has not been generally adopted due to the relatively high levels needed and uncertain effects obtained.
There thus remains a need for a consistent, easily applied and economically feasible method to enhance mechanical separation techniques either through enhanced component separation or increased throughput.